This project is for the conduct of a survey of a Norwegian population to obtain a 25-year follow-up periodontal examination of a large number of an original cohort who participated in the first examination sequence of the Natural History of Periodontal Disease Study (NHPD), begun in 1969 in Oslo, Norway. The NHPD study is unique in that no other comparable study cohort exists for which longitudinal clinical periodontal measurements are available over a 20-year period in terms of length of follow-up and potential for future follow-up. Currently, six sequential periodontal assessments for these participants are available, spanning 19 years, for a substantial cohort of the original participants. Microbial assays specific for P. gingivalis, P. intermedia, Actinobacillus antinomycetemcomitans, and others to be specified will be conducted as part of this examination for 30 participants, 15 of whom are found to have severe disease and 15 controls. Paper point samples will also be collected from all subjects at mesio-buccal sites of molars and properly stored.